Single-shot videography of electron number density evolution in an atmospheric nanosecond gas discharge via interferometric FRAME

A comprehensive investigation of the spatiotemporal profile of electron number density is crucial for elucidating the physicochemical processes governing gas discharges. In particular, for streamers, the electron number density plays a decisive role, directly influencing streamer propagation and development. Most of the non-invasive electron number density measurements, such as Thomson scattering, Stark broadening, and microwave interferometry, are typically limited to pointwise or one-dimensional measurements and often require multiple exposures. These limitations hinder their applicability to streamer studies, where significant shot-to-shot variability, especially at atmospheric pressure, makes single-shot diagnostics highly desirable. In this work, we present an interferometry-based laser diagnostic technique to capture the evolution of electron number density in a nitrogen streamer initiated by a 4-ns nanosecond pulsed discharge in a pin-to-pin electrode configuration. By employing a femtosecond laser with a diagnostic method called Frequency Recognition Algorithm for Multiple Exposures (FRAME), we achieved more than 10 GHz temporal resolution, enabling the capture of rapid streamer dynamics within a single camera acquisition. Furthermore, two-dimensional streamer simulations are performed to validate the measured electron density evolution and to assess the roles of electron impact ionization, excitation, and attachment during streamer development.